Classical philosophy and Darwinian biology are far more compatible than is usually assumed. In fact, looking at either from the standpoint of the other can enrich and deepen our appreciation of both. From a Darwinian point of view, the theories of Plato and Aristotle deserve to be taken very seriously. From the classical point of view, Darwinian biology is much less reductionist than its enemies suppose.

Saturday, April 4, 2015

Borges, Plato, & Natural Selection

Tomas Luis Borges had an
astonishing genius for channeling vast currents in the history of ideas into
the narrow stream of a compelling story. One of his most frequently mentioned stories
was “The Library of Babel”.It begins
with these words:

The universe (which others call the Library) is composed of an
indefinite and perhaps infinite number of hexagonal galleries, with vast air
shafts between, surrounded by very low railings. From any of the hexagons one
can see, interminably, the upper and lower floors. The distribution of the
galleries is invariable. Twenty shelves, five long shelves per side, cover all the
sides except two; their height, which is the distance from floor to ceiling,
scarcely exceeds that of a normal bookcase. One of the free sides leads to a
narrow hallway which opens onto another gallery, identical to the first and to
all the rest.

If you haven’t read the story, I
am about to do you the terrible disservice of spoiling the end.I can only offer the defense that many more
people have read about the story than have actually read the story.

The library consists of a vast
but not infinite set of books.

There are five shelves for each of the hexagon's walls; each
shelf contains thirty-five books of uniform format; each book is of four
hundred and ten pages; each page, of forty lines, each line, of some eighty
letters which are black in color. There are also letters on the spine of each book;
these letters do not indicate or prefigure what the pages will say… Second: The
orthographical symbols are twenty-five in number.

The library consists of all the
books that are logically possible, given the parameters just listed.To say that this library would be vast is
meaningful only in the strictest mathematical sense.It would be, to say the least, astronomical
in extent.Consider that in this library
somewhere is a perfect copy of Shakespeare’s Richard III.There is also a copy of Dickey Three with
alternative endings, including one in which the villain is rescued by the
Mighty Morphin’ Power Rangers.There are
perfectly accurate histories of the life of every single human being and indeed
every single organism along with alternative histories.In one of them I am married to two Victoria’s
Secret models.

Of course, all of the coherent
reads will be only a drop in the bucket.Most of the books will be incoherent jumbles of nonsense.One of the books will consist of nothing but
the word “word” over and over again.

This brilliant thought problem,
in the form of a librarian’s musings on the bizarre world that he inhabits, is
another version of the infamous infinite monkey theorem.Could a set of monkeys (say 100), typing
randomly, eventually produce a copy of Richard III?According to the theorem, which I believe to
be logically sound, the answer is “yes, given enough time”.However, the time required is unimaginably
vast.Even to produce “Now is the winter
of our discontent” would require more time, I recently calculated, than the age
of the Kosmos itself.Along the way you
would get a vast number of half finished, garbled, and alternative
versions.

Darwin’s great idea was to
explain how you could get Shakespeare himself out of processes just as random
as our team of monkeys or Borges’ library.All you need is some device that persistently steers the primates in the
right direction.If the monkeys keep
typing now is the winter over and
over again until they get the next letter right and then keep typing that…That is what natural selection does.

These reflections were set in
motion by wonderful essay in Aeon.Andreas Wagner, professor in the Institute of Evolutionary Biology and
Environmental Studies at the University of Zurich and at the Santa Fe Institute
in New Mexico, argues that Darwinian evolution could not work without “nature’s
library of Platonic forms.”

How do random DNA changes lead to innovation? Darwin’s concept
of natural selection, although crucial to understand evolution, doesn’t help
much. The thing is, selection can only spread innovations that already exist.
The botanist Hugo de Vries said it best in 1905: ‘Natural selection can explain
the survival of the fittest, but it cannot explain the arrival of the fittest.’…

A metaphor might help to clarify the problem. Imagine a giant
library of books containing all possible sequences of letters in the alphabet.
Such a library would be huge beyond imagination, and most of its texts would of
course be pure gibberish. But some would contain islands of intelligibility – a
word here, a Haiku there – in a sea of random letters. Still others would tell
all stories real and imagined: not only Dickens’s Oliver Twist or Goethe’s
Faust, but all possible novels and dramas, the biography of every single human,
true and false histories of the world, of other worlds as yet unseen, and so
on. Some texts would include descriptions of countless technological
innovations, from the wheel to the steam engine to the transistor – including
countless innovations yet to be imagined. But the chances of choosing such a
valuable tome by chance are minuscule.

That giant library is, of course,
Borges’ library, though Wagner doesn’t give credit here.He does present the same problem.

A protein is a volume in a library just like
this, written in a 20-letter alphabet of amino acids. And while protein texts
might not be as long as Tolstoy’s War and Peace, their total number is
still astonishing. For example, a library of every possible amino acid string
that is 500 letters long would contain more than 10600 texts – a one
with 600 trailing zeros. That vastly outnumbers the atoms in the visible
universe.

The library is a giant space of the possible, encoding all the
proteins that could be useful to life. But here’s the thing: evolution can’t
simply look up the chemicals it needs in a giant catalogue. No, it has to inch
its way painstakingly along the stacks.

So how does natural selection
find the next viable protein sequence?How does this mindless process find the path that arrives at viable
minds?

For more than a decade, this endeavour has
been a focus of my research at the University of Zurich and at the Santa Fe
Institute in the US. We evolve molecules in the laboratory and record their
journey through these libraries, together with any new and useful texts they
find. We also map the locations of millions of molecules that nature’s
populations have discovered in their billion-year journey. We use powerful
computer simulations to explore those parts of a library that nature has not
yet discovered. Through these efforts, we and others have found a system of
organisation in these libraries that is as strange as it is perfect for
guideless exploration.

One of its features is easily explained once
we observe that neighbouring texts in nature’s library have similar letter
sequences, and the closest texts – immediate neighbours – differ in just a
single letter.

If natural selection had to pick
at random from the possible protein sequences, no conceivable time would
suffice for evolutionary processes. But
it didn’t have to do that.The basic
molecules on which natural selection works (at the molecular level) open up a
large but not vast number of pathways.Many
different directions are open, but only so many.A library of possible forms is on the same shelf
and it is a big shelf, but manageable.Certain pathways prove very fruitful, and natural selection moves up and
down them again and again. Many
different combinations of genes work the same outcomes along a viable
pathway.

The remarkable thing is, having so many
different ways to say the same thing means that there are many more possible
slips of the tongue. And with each slip of the tongue comes the possibility of
saying something different. Just as the word GOLD emerges from a single letter
change in MOLD, some neighbours of a text express new meanings. And as the
browsers work their way through each synonym for some original text, different
innovations become accessible. By creating safe paths through the library,
genotype networks create the very possibility of innovation.

Let me put this point as strongly as I can.
Without these pathways of synonymous texts, these sets of genes that express
precisely the same function in ever-shifting sequences of letters, it would not
be possible to keep finding new innovations via random mutation. Evolution
would not work.

What Wagner thinks, if I read him
right, is that the molecular material that natural selection began to work on
from the very beginning of life on earth already contained a large but manageable
set of forms.If it hadn’t, evolution
could not have been possible.He
recognizes this library of viable forms to be Platonic.That makes two of us.